Packaging materials, packages and processes which employ a layer of tacky or pressure sensitive adhesive to effect opening and reclosure features are known, but they are problematical or disadvantageous for various reasons. U.S. Patents which disclose such materials and packages are U.S. Pat. Nos. 3,454,210, 5,089,320 and 5,382,472.
U.S. Pat. No. 3,454,210 discloses packages made from a base web having a pressure sensitive adhesive layer all over it and which is covered by a bondable, rupturable film, which in turn is bonded to a base film to form the package. The package is opened by rupturing the rupturable film and pulling it from the pressure sensitive adhesive layer. This leaves a surface of pressure sensitive adhesive exposed and against which the web can be pressed to reseal the package.
A main disadvantage of the packaging materials and packages disclosed in U.S. Pat. No. 3,454,210 is that the entire web of the entire package carries the layer of the pressure sensitive adhesive. Since pressure sensitive adhesives are only needed where opening is to be effected, and since they are expensive materials, this approach is wasteful and excessively expensive. Also, pressure sensitive adhesives tend to give off objectionable odors which can be imparted to the packaged products, e.g. to food, and can be sensed by the consumer upon and after opening. The use of such adhesives on the entire packaging material magnifies the odor problem.
U.S. Pat. No. 5,089,320 discloses a similar flexible packaging material which is heat sealable to itself. The packaging material has a layer of tacky adhesive sandwiched between a skin layer of a heat sealable polymer and a substrate. The tacky adhesive is distributed throughout the material. The patent also discloses that since the tacky adhesive is required only in the area where the package is to be opened, the adhesive may be coated onto the substrate in register only where it is required. The skin layer may be similarly applied in register over the adhesive alone, such as by printing the adhesive layer and the skin layer onto the substrate sequentially using a central impression press. The skin layer may be applied to the other surface of areas of the substrate as well, including the entire surface of the packaging material. The patent also discloses the tacky adhesive may also be applied to the substrate by transferring it from the carrying medium and the skin may be transferred with the adhesive by this technique. The technique is known for transferring a thin layer of vapor deposited metal from one substrate to another. The carrying medium preferably is paper, coated on one or both sides with a silicone release agent. The paper carrier may be recycled or may be an endless belt for a continuous process.
The approach disclosed in U.S. Pat. No. 5,089,320 of distributing the tacky adhesive throughout the packaging material is disadvantageous for the reasons stated previously. Coating the tacky adhesive onto the substrate only where it is needed is disadvantageous because it requires extra and specially designed equipment for coating and aligning the tacky adhesive and the heat sealable skin layer. Also, registering the skin layer with the tacky adhesive and applying the coatings sequentially is complex and involves extra steps. Alignment and off-registration problems can occur. Applying the tacky adhesive with or without a skin layer from a carrier requires a carrier system and involves disposing of and wasting the paper carrier, or recycling it, special silicone coatings and equipment, and carrier conveying equipment.
U.S. Pat. No. 5,382,472 discloses a resealable packaging material made by side-by-side simultaneous coextrusion of several thermoplastic resins through a die to form a film having two or more bands of material which extend in the machine direction. The first band contains conventional packaging polymers and no pressure sensitive adhesive, and, the second band includes a surface layer of heat sealable polymer, a core layer of pressure sensitive adhesive and a layer of thermoplastic resin adjacent the layer. In the disclosed side-by-side coextruded film, the bands are alongside one another and the second band is the same thickness as the first band. The surfaces of the second band are shown as being co-planar with the surfaces of the first band. Each band extends from one surface of the side-by-side coextruded film to the other surface of the film. The film is folded upon itself and heat sealed to form a package by sealing jaws acting on the heat sealable polymer in the second band. When the heat seal is pulled apart, the heat seal layer ruptures through to the pressure sensitive adhesive and delaminates from it. The rupturing and delamination occur within the surface boundaries of the side-by-side coextruded film.
The approach disclosed in U.S. Pat. No. 5,382,472 is disadvantageous in several respects. It is limited in that the coextruded film can only be made by side-by-side coextrusion. Side-by-side coextrusion in turn is limited in that the side-by-side die is designed to run only certain resins. Even if it is designed to run a variety of resins, each die is configured to place the second band in a fixed location. To change the location of the second band, a new die is needed. To make adjustments within a given die to suit a resin or various resins is problematical and can result in surface non-uniformity of thickness of the first and second bands. Even a small difference in thickness of the second band will result in a raised area or hollow area along one side of the surface of a roll of the side-by-side coextruded film. To minimize this surface non-uniformity on a roll, roll size for shipments to customers will be kept relatively small. This will cause more frequent roll changes than desired.
Another approach which employs a tacky adhesive to provide an opening feature for a flexible package is that wherein an elongated cut is made through a packaging film. The cut is widened and a reclose tape wider than the cut and made of a substrate layer and a tacky adhesive layer is fed by a carrier system and applied with the tacky adhesive side down to the film to cover the open cut. The film is folded over on itself and pressed together without heat to adhere the tacky adhesive through the open cut to the opposite wall of the film. To open the package, the tape's tacky adhesive is pulled away from the opposite wall of the package.
This approach is disadvantageous because it requires that the tape's tacky adhesive layer be treated or covered with a removable release layer, or carried on a silicone coated paper carrier layer. These treatment systems and removable cover or carrier systems add steps, equipment and expense to produce the tape and package. Also, the oriented polyethylene terephthalate (PET) or polypropylene (PP) used as the substrate layer, are relatively expensive materials, cutting the film can effect the integrity and barrier properties of the film, and the seal obtained merely by pressing the adhesive against the film is not hermetic and has not been tamper evident.
It is an object of this invention to provide packaging materials, packages and methods which overcome the above and other problems and disadvantages existing in the art.
Accordingly, it is an object of this invention to provide an elongate multilayer flexible heat sealable, peelable and reclosable strip which is comprised of a tacky adhesive layer and which is suitable for being applied to a packaging film and heat sealed to it to form a package whose heat seal is manually readily openable and reclosable.
Another object is to provide packaging materials comprised of packaging films having the strip secured thereto, packages made from these packaging materials and methods for forming the same.
The elongate strip of this invention solves the above and other problems in the art. The strip which includes a layer of the sometimes odiferous tacky adhesive is thin, narrow and applied only where the opening and reclose feature is needed. Therefore, adhesive cost and objectionable odor problems are minimized. Since the strip includes one or more layers already covering the tacky adhesive layer, complicated steps involved in registering, aligning and applying a cover layer over or with the tacky adhesive layer, such as required in a coating process do not exist. Special treatment and removable cover or carrier systems are not required. Also, special and inherently limited side-by-side coextrusion dies and processes are not needed. Existing conventional equipment and processes can be employed for forming wide multilayer webs comprising the layer materials of the strip of this invention. The surface of a roll of strip cut from the web and wound on the roll will be uniform, and roll size in terms of linear feet of a strip will be at least the same, or greater than that of a roll of the packaging film to which the strip will be applied. The strip provides great flexibility of use. One or more strips can be applied at any desired location(s) on a packaging film and a strip can be adapted to be applied to many different packaging films and combinations of films having different surface layers, characteristics and requirements. Accordingly, the strips can be employed on a wide variety of films available from different suppliers. Packagers are not limited to using only side-by-side coextruded webs available from only limited suppliers. The strips and the packaging materials bearing the strips form packages whose heat seals are hermetic and can include tamper evident features.
The foregoing and other objects, features and advantages of this invention will be evident and further appreciated from the following description and accompanying drawings.